Lamp circuit limited to a booster in which the power output decreases with increasing frequency

Abstract

A power supply circuit (100) for use in driving fluorescent lamps (102, 104, 106) has a current mode control voltage boost IC (144) which produces a boosted voltage and has a power control input (pin 3) and a frequency control input (pin 4). The lamps are driven by a self oscillating inverter (178, 180, 196, 198) which is powered from the voltage boost IC and which operates at a frequency independent therefrom. In order to dim the lamps a D.C. bias voltage is applied to the power control input. At the same time a commensurate D.C. bias voltage is applied to the frequency control input so as to provide power factor correction in dependence on the power produced by the voltage boost IC. The circuit thus provides a substantially constant, optimum power factor at both full and dimmed light levels.

I claim: 
     
       1. A power supply circuit for producing different power levels comprising: an input coupled to a source of AC power;   a rectifier, having two rectifier input terminals and two rectifier output terminal, the rectifier input terminals coupled to the input;   a first switch coupled between the input and the rectifier;   voltage boost means, coupled to the rectifier output terminals, for producing a boosted voltage, the voltage boost means having a power control input and a frequency control input;   power control means coupled to the power control input of the voltage boost means for controlling, in response to a signal, the current produced by the voltage boost means, and thereby the power produced by the power control means, the power control means having a power control input terminal; and   frequency control means coupled to the frequency control input of the voltage boost means for controlling the frequency of operation thereof in dependence on the power produced by the voltage boost means, such that when the power produced by the voltage boost means is decreased the frequency of operation of the voltage boost means is increased, and that when the power produced by the voltage boost means is increased, the frequency of operation of the voltage boost means is decreased, so as to provide power factor correction in dependence on the power produced by the voltage boost means; and   a second switch, coupled in series between one rectifier input terminal and the power control input terminal, for generating a signal to the power control means to change the illumination level of the lamp, the power control means coupled to one rectifier output terminal.   
     
     
       2. A power supply circuit according to claim 1 wherein the voltage boost means comprises a current mode control circuit. 
     
     
       3. A power supply circuit according to claim 1 wherein the power control means comprises first D.C. bias means for applying a first D.C. bias to the current control input of the voltage boost means to control the power produced thereby. 
     
     
       4. A power supply circuit according to claim 1 wherein the frequency control means comprises second D.C. bias means for applying a second D.C. bias to the frequency control input of the voltage boost means to control the frequency of operation thereof. 
     
     
       5. A power supply circuit according to claim 1 further comprising D.C. supply means, and wherein the power control means comprises first D.C. bias means for applying a first D.C. bias derived from the D.C. supply means to the current control input of the voltage boost means to control the power produced thereby; and   the frequency control means comprises second D.C. bias means for applying a second D.C. bias derived from the D.C. supply means to the frequency control input of the voltage boost means to control the frequency of operation thereof.   
     
     
       6. A circuit for driving a gas discharge lamp load at different illumination levels, the circuit comprising: an input coupled to a source of AC voltage;   a rectifier having at least one rectifier input terminal and at least one rectifier output terminal, the rectifier input terminal coupled to the input;   voltage boost means coupled to the rectifier output terminal for producing a boosted voltage, the voltage boost means having a power control input and a frequency control input;   power control means coupled to the power control input of the voltage boost means for controlling, in response to a signal, the current produced by the voltage boost means, and thereby the power produced by the voltage boost means, the power control means being coupled to the rectifier output terminal; and   frequency control means coupled to the frequency control input of the voltage boost means for controlling the frequency of operation thereof in dependence on the power produced by the voltage boost means, such that when the power produced by the voltage boost means is decreased the frequency of operation of the voltage boost means is increased, and that when the power produced by the voltage boost means is increased, the frequency of operation of the voltage boost means is decreased, so as to provide power factor correction in dependence on the power produced by the voltage boost means;   a switch, coupled to the rectifier input terminal, for generating the signal to the power control means to change the illumination level of the lamps; and   oscillator means powered by voltage boost means for producing a output signal to drive the gas discharge lamp load, the frequency of the oscillator means output signal being substantially independent of the frequency of operation of the voltage boost means.   
     
     
       7. A circuit according to claim 6 wherein the voltage boost means comprises a current mode control circuit. 
     
     
       8. A circuit according to claim 6 wherein the power control means comprises first D.C. bias means for applying a first D.C. bias to the current control input of the voltage boost means to control the power produced thereby. 
     
     
       9. A circuit according to claim 6 wherein the frequency control means comprises second D.C. bias means for applying a second D.C. bias to the frequency control input of the voltage boost means to control the frequency of operation thereof. 
     
     
       10. A power supply circuit according to claim 6 further comprising D.C. supply means, and wherein the power control means comprises first D.C. bias means for applying a first D.C. bias derived from the D.C. supply means to the current control input of the voltage boost means to control the power produced thereby; and   the frequency control means comprises second D.C. bias means for applying a second D.C. bias derived from the D.C. supply means to the frequency control input of the voltage boost means to control the frequency of operation thereof.   
     
     
       11. A power supply circuit for producing different power levels comprising: an input coupled to a source of AC power;   a rectifier, having two rectifier input terminals and two rectifier output terminal, the rectifier input terminals coupled to the input;   a first switch coupled between the input and the rectifier;   voltage boost means, coupled to the rectifier output terminals, for producing a boosted voltage, the voltage boost means having a power control input and a frequency control input, the frequency control input and the power control input being separate inputs;   power control means coupled to the power control input of the voltage boost means for controlling, in response to a signal, the current produced by the voltage boost means, and thereby the power produced by the power control means, the power control means having a power control input terminal; and   frequency control means coupled to the frequency control input of the voltage boost means for controlling the frequency of operation thereof in dependence on the power produced by the voltage boost means, such that when the power produced by the voltage boost means is decreased the frequency of operation of the voltage boost means is increased, and that when the power produced by the voltage boost means is increased, the frequency of operation of the voltage boost means is decreased, so as to provide power factor correction in dependence on the power produced by the voltage boost means; and   a second switch, coupled in series between one rectifier input terminal and the power control input terminal, for generating a signal to the power control means to change the illumination level of the lamp, the power control means coupled to one rectifier output terminal.   
     
     
       12. A power supply circuit according to claim 1 wherein the voltage boost means comprises a current mode control circuit. 
     
     
       13. A power supply circuit according to claim 1 wherein the power control means comprises first D.C. bias means for applying a first D.C. bias to the power control input of the voltage boost means to control the power produced thereby. 
     
     
       14. A power supply circuit according to claim 1 wherein the frequency control means comprises second D.C. bias means for applying a second D.C. bias to the frequency control input of the voltage boost means to control the frequency of operation thereof. 
     
     
       15. A power supply circuit according to claim 1 further comprising D.C. supply means, and wherein the power control means comprises first D.C. bias means for applying a first D.C. bias derived from the D.C. supply means to the power control input of the voltage boost means to control the power produced thereby; and   the frequency control means comprises second D.C. bias means for applying a second D.C. bias derived from the D.C. supply means to the frequency control input of the voltage boost means to control the frequency of operation thereof.